2012-09-05

Timing and LTE - SONET, GPS or IEEE1588v2?

LTE has been rapidly moving towards a packet based backhaul network, while still trying to cope with a dated and inadequate timing model based on TDM. Timing is necessary for both 3G and 4G deployments. Today, timing is typically delivered by either a SONET/SDH-based T1/E1 line or from GPS satellites. SONET/SDH is not only expensive, but also inadequate for next-generation wireless networks, since it can only deliver frequency synchronization, but not the time-of-day (ToD) synchronization that is mandatory for TD-LTE and LTE-Advanced (LTE-A) – the “true 4G.”

IEEE 1588v2 promises a simple, low-cost option for packet network timing upgrades and an ideal alternative and backup to GPS for TD-LTE and LTE-A networks. In many instances, full IEEE 1588v2 awareness is only needed right at the base station or cell site where timing needs to be provided to the cell. Within the many hops in the network along the way, Transparent Clocks provide the most cost effective way to upgrade the network to LTE and LTE-Advanced simply by replacing port-level PHYs with new devices such as the ones from Vitesse, that can implement a nanosecond-accurate and highly stable time-of-day forwarding architecture, while fully compensating for transit time and PDV.\